Molecular Structure Determination by EXAFS of [Y(NCS)6]3- Units in Solid State and in Solution. A Comparison with Density Functional Theory Calculations

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1998-09, Vol.102 (38), p.7435-7441
• Main Authors: Díaz-Moreno, Sofía, Martínez, José M, Muñoz-Páez, Adela, Sakane, Hideto, Watanabe, Iwao
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp982125k

The structure of one of the rare octahedral Y3+ complexes, hexakis(thiocyanato-N)yttrate(III), has been elucidated with extended X-ray absorption fine structure (EXAFS) spectroscopy and confirmed by density functional theory (DFT) calculations. The analysis of EXAFS spectra indicates coordination through nitrogen atoms, already suggested by IR and NMR data, and provides information about the linear arrangement of the NCS- ligands with the yttrium atoms inside the complex. This arrangement emphasizes multiple scattering contributions to the EXAFS signal, due to the focusing scattering effect, and allows the accurate determination of the structure of the whole complex up to the third coordination shell, which is distant by more than 5 Å from the absorbing atom, Y, a resolution without precedent in the use of the technique. The best reproduction of the solid state and acetonitrile solution spectra was achieved with the same structure:  a symmetric octahedron with coordination distances equal to 2.36(1), 3.5(1), and 5.1(2) Å for Y−N, Y−C, and Y−S shells, respectively, the only difference between both spectra being the higher dynamic disorder of the solution spectrum. DFT calculations predict this geometry as the most stable, discarding other arrangements in which the coordinating atom is sulfur. The agreement between EXAFS data and DFT optimized structure is quite high, and differences between predicted and experimental IR bands are below 5%.